Article IV, Section 1 of the United States Constitution, known as the "Full Faith and Credit Clause", addresses the duties that states within the United States have to respect the "public acts, records, and judicial proceedings of every other state." According to the Supreme Court, there is a difference between the credit owed to laws (i.e. legislative measures and common law) as compared to the credit owed to judgments.[1] Judgments are generally entitled to greater respect than laws, in other states.[2] At present, it is widely agreed that this Clause of the Constitution has little impact on a court's choice of law decision,[3] although this Clause of the Constitution was once interpreted differently.[4]

Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State. And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.

A similar clause existed in Article IV of the Articles of Confederation, the predecessor to the U.S. Constitution: "Full faith and credit shall be given in each of these States to the records, acts, and judicial proceedings of the courts and magistrates of every other State."[5] A Pennsylvania court explained in 1786 that this provision in the Articles of Confederation did not direct that "executions might issue in one state upon the judgments given in another", but rather was "chiefly intended to oblige each state to receive the records of another as full evidence of such acts and judicial proceedings."[6]

At the Philadelphia Convention, James Madison said that he wanted to supplement that provision in the Articles of Confederation, to let Congress "provide for the execution of Judgments in other States, under such regulations as might be expedient."[7] By September 1, 1787, negotiations at the Constitutional Convention had led to the following draft which included supplementary language as Madison had requested:[8]

Full faith and credit ought to be given in each state to the public acts, records, and judicial proceedings, of every other state; and the legislature shall, by general laws, prescribe the manner in which such acts, records, and proceedings, shall be proved, and the effect which judgments, obtained in one state, shall have in another.

After several further modifications, the Full Faith and Credit Clause assumed the form in which it remains today. During the ratification process, James Madison remarked further on this subject, in Federalist No. 42. He wrote that the corresponding clause in the Articles of Confederation was "extremely indeterminate, and can be of little importance under any interpretation which it will bear."[9] Of the expanded clause in the Constitution, Madison wrote that it established a power that "may be rendered a very convenient instrument of justice, and be particularly beneficial on the borders of contiguous States."[9]

In 1790, shortly after the Constitution had been ratified, Congress took action under the Full Faith and Credit Clause, enacting that "the records and judicial proceedings, authenticated as aforesaid, shall have such faith and credit given to them in every Court within the United States, as they have by law or usage in the Courts of the state from whence the said records are or shall be taken."[10] In 1813, the Supreme Court interpreted this federal statute, in the leading case of Mills v. Duryee.[11] Justice Joseph Story wrote for the Court that it was the federal statute (rather than the constitutional provision) that made records from one state effective in another state:

It is argued, that this act provides only for the admission of such records as evidence, but does not declare the effect of such evidence, when admitted. This argument cannot be supported. The act declares, that the record, duly authenticated, shall have such faith and credit as it has in the state court from whence it is taken. If in such court it has the faith and credit of evidence of the highest nature, viz., record evidence, it must have the same faith and credit in every other court.

Although the Court was engaged in statutory interpretation in Mills, the Court eventually characterized Mills as a constitutional decision, in the 1887 case of Chicago & Alton v. Wiggins.[12] During the following decades and centuries, the Supreme Court has recognized a "public policy exception" to both the Full Faith and Credit Clause and the accompanying federal statute. In 1939, the Court in Pacific Employers Insurance v. Industrial Accident wrote:

[T]here are some limitations upon the extent to which a state may be required by the full faith and credit clause to enforce even the judgment of another state in contravention of its own statutes or policy. See Wisconsin v. Pelican Insurance Co., 127 U.S. 265; Huntington v. Attrill, 146 U.S. 657; Finney v. Guy, 189 U.S. 335; see also Clarke v. Clarke, 178 U.S. 186; Olmsted v. Olmsted, 216 U.S. 386; Hood v. McGehee, 237 U.S. 611; cf. Gasquet v. Fenner, 247 U.S. 16. And in the case of statutes...the full faith and credit clause does not require one state to substitute for its own statute, applicable to persons and events within it, the conflicting statute of another state, even though that statute is of controlling force in the courts of the state of its enactment with respect to the same persons and events.[13]

The Supreme Court continues to apply its public policy exception differently for state judgments as compared to state laws. In the 2003 case of Franchise Tax Board v. Hyatt, the Court reiterated that, "[o]ur precedent differentiates the credit owed to laws (legislative measures and common law) and to judgments."[1]

If the legal pronouncements of one state conflict with the public policy of another state, federal courts in the past have been reluctant to force a state to enforce the pronouncements of another state in contravention of its own public policy. In cases of out-of-state judgments, the Court has stated that there may be exceptions to the enforcement and jurisdiction of out-of-state judgments, but maintains that there is no public policy exception to the Full Faith and Credit Clause for judgments.[14]

Federal statutory law (28 USC § 1738) provides that:

Such Acts, records and judicial proceedings or copies thereof, so authenticated, shall have the same full faith and credit in every court within the United States and its Territories and Possessions as they have by law or usage in the courts of such State, Territory or Possession from which they are taken.[15]

Until the Supreme Court struck down all laws banning interracial marriage in 1967, a number of states banned interracial marriage and did not recognize marriage certificates issued in other states for interracial couples. The full faith and credit clause was never used to force a state to recognize a marriage it did not wish to recognize.[16] However, the existence of a common-law marriage in a sister state (still available in nine states and the District of Columbia) has been recognized in divorce or dissolution of marriage cases.

The clause's application to state-sanctioned same-sex marriages, civil unions, and domestic partnerships is unresolved, although the case of marriage has been rendered moot. In 1996 the U.S. Congress specifically passed a statute, known as the Defense of Marriage Act, which stated that states need not recognize same-sex marriages performed outside the state; this is interpreted to relieve states of their duty[citation needed] under the Full Faith and Credit clause. Between 1996 and 2004, 39 states passed laws and constitutional amendments that defined marriage as consisting solely of different-sex couples[citation needed], most of which also explicitly prohibited the state from honoring same-sex marriages performed in other states and countries[citation needed]. Many of these state laws were struck down in federal courts[citation needed], until the Supreme Court in Obergefell v. Hodges (2015) made same-sex marriage legal in all U.S. states and territories. However, Obergefell did not rely on the Full Faith and Credit clause, but instead concluded

The Court, in this decision, holds same-sex couples may exercise the fundamental right to marry in all States. It follows that the Court also must hold—and it now does hold—that there is no lawful basis for a State to refuse to recognize a lawful same-sex marriage performed in another State on the ground of its same-sex character.

The clause is not applied to prohibited degrees of kinship (including cousin marriage), and couples moving from a state where cousin marriage is allowed to one where it is prohibited or a criminal offense risk loss of benefits or criminal prosecution if moving to another state, although this is rarely enforced or discovered until legal conflicts arise.

In March 2016, the Supreme Court ruled in V.L. v. E.L. that under the Full Faith and Credit Clause, the State of Alabama must recognize the adoption decree granted to a same-sex couple by a Georgia state court in 2007, regardless of how that court came to its conclusion granting the decree.

^Alaska Packers v. Industrial Accident Commission, 294U.S.532 (1935) (holding that full faith and credit may require application of law of the state with the greatest interest in the case); See Reese, Legislative Jurisdiction, 78 Colum. L. Rev. 1587 (1978).

^Act of May 26, 1790 titled, "An Act to Prescribe the Mode in Which the Public Acts, Records, and Judicial Proceedings in Each State, Shall Be Authenticated So As to Take Effect in Every Other State." The 1790 act was the progenitor of an act that is codified at 28 U.S.C.§ 1738. The current act was amended in 1948 to give state statutes the same interstate effect as state judgments.

^Chicago & Alton v. Wiggins, 119U.S.615 (1887): "Without doubt the constitutional requirement (article 4, 1) ... implies that the public acts of every state shall be given the same effect by the courts of another state that they have by law and usage at home. This is clearly the logical result of the principles announced as early as 1813, in Mills v. Duryee, 7 Cranch, 481, and steadily adhered to ever since."